Hospital acquired pneumonia costs up to 2 billion dollars per year in the United States, and any inexpensive therapy which reduces this septic complication could greatly impact health care costs. Enteral feeding significantly reduces the complications of pneumonia compared with intravenous (IV-TPN) feedings by 60-70 percent in trauma patients. Our experimental and clinical work implicates previously unrecognized defects in mucosal immunity which develop when the intestinal tract is not stimulated with enteral feeding or when surrogates of enteral feeding are not provided. The principal specific immunologic defense at mucosal surfaces is secretory IgA produced by the mucosal-associated lymphoid tissue (MALT). The principal anatomic site for immunologic sensitization of Peyer's patches within the small intestine. Adhesion molecules direct unsensitized immunocytes through the Peyer's patches where these lymphocytes are sensitized and change their own surface integrins. They are then directed to both intestinal and extraintestinal sites, such as the respiratory tract, where they produce IgA against those antigens. The antibody binds to bacteria, preventing their attachment and their ability to infect. This proposal focuses on how route and type of nutrition affects the expression of the specific adhesion molecules, modified MAdCAM-1, unmodified MAdCAM-1, and ICAM-1 which are important in directing unsensitized immunocytes into Peyer's patches. The proposal tests the hypothesis that interaction between these adhesion molecules and their ligands on naive T and B cells are critical in maintaining mucosal immunity in both intestinal and extraintestinal sites. The proposal is designed to test the hypothesis that inhibition of these interactions recreates the defects in in vivo mucosal defenses that are induced when enteral feeding is not provided. It also focuses on previous observations that a specific immunocyte fuel, glutamine, and the enteric nervous system neuropeptide, bombesin, can act as surrogates for enteral feeding and exert beneficial effects upon the MALT in IV-TPN-fed animals by upregulating MAdCAM-1 and ICAM- 1 expression. The experiments are designed to confirm that IgA is a critical element of specific immunity and respiratory defenses against pneumonia with in vivo experiments. These experiments use a monoclonal antibody produced by a hybridoma cell line which is specific for polysaccharide antigen(s) found on a high percentage of clinical isolates of Pseudomonas aeruginosa.